Pain and neural transmission Flashcards
Name some somatosensory receptors in the skin
- Meissner corpuscle
- Pacinian corpuscle
- Ruffini’s corpuscles
- Merkel’s disks
- Free nerve endings
Where are sensory receptors detecting light touch located?
Closer to the surface
Which sensory receptor detect pain?
Free nerve endings: Nociceptors
Where are free nerve endings found?
In the top layer of the dermis and the epidermis
Where are Nociceptors found?
In the periphery as simple free nerve endings.
How do Nociceptors terminate in the dermis?
Peripheral nerve fibre branches & terminates as naked, unmyelinated endings in dermis.
What does naked mean when describing nerves?
Means the nerves are unmyelinated
Can a pain response be initiated only by the stimulation of a pain receptor?
No you need to induce other things and release other substances
What does tissue damage and inflammation trigger?
release of substances e.g prostaglandins, bradykinin and histamine that can sensitize peripheral nociceptors and induce hyperalgesia.
What can chemical mediators like prostaglandins, bradykinin and histamine do?
They can can sensitize peripheral nociceptors and induce hyperalgesia.
What is hyperalgesia
Induces more pain (ie increasing the pain response)
What do we need to initiate hyperalgesia?
Need free nerve ending and the relapse of chemical mediators at the site of damage
Why do we need an increased pain response?
It is like positive feedback as the pain will stop us from harming the area further
What occurs in free nerve endings?
Transduction of painful stimuli
Where does the Transduction of painful stimuli occur?
Occurs in the free nerve endings of unmyelinated ‘C’ fibres and thinly myelinated ‘Ad’ fibres.
What are the 2 types of pain fibres?
Some nociceptors only respond to ONE modality
Most nociceptors are POLYMODAL and respond to mechanical thermal and chemical stimuli
What are some modalities nociceptors can respond to?
1, Mechanical response to strong pressure
- Thermal response to burins heat or extreme cold
- Chemical response to histamine or other chemicals
Where are Thermoreceptors found?
Deep in the epidermis
What do Thermoreceptors respond to?
Warm or cold stimuli
What type of receptors do Thermoreceptors have?
Bare nerve endings
Where are nociceptors found?
In the epidermis
What type of receptors do nociceptors have?
Bare nerve endings
Describe how are sensory transduction occurs
- Stimulus deforms or changes the nerve ending.
- This Alters the membrane permeability of the receptor membrane.
- This then Produces a receptor (generator) potential.
- This Triggers an action potential which travels along the axon to the CNS.
Name the cells and fibres involved in a sensory transaction
- Receptor endings
- Pain and temperature afferent fibres
- Mechanosensory afferent fibres
- Dorsal rot ganglion
- Spinal cord
How can we see how the nociceptors are distributed in the skin?
By using a technique called microneurography
What is microneurography?
Recording Transcutaneous nerves in humans
What are the 3 steps involved in microneurography?
- Thermal stimuli applied to receptive field of cutaneous thermoreceptor and nociceptor
- Record afferent firing in response to incremental temperatures
- Graph plotting afferent firing frequency versus temperature
What type of fibres make up Thermoreceptors sensitive to high temperatures?
C fibres
What type of fibres make up Thermoreceptors sensitive to low temperatures?
A Delta fibres
What type of fibres make up Nociception sensitive to sharp pain?
A Delta fibres
What type of fibres make up Nociception sensitive to burning pain?
C fibres
Which fibres are found in the tooth pulp?
Mostly A delta and c fibres but not all of them are pain fibres
Generally what do nerve fibres with larger diameters tend to be associated with?
Large diameters mean the nerve impulse with be more rapidly conducted
This is associated with low threshold mechanoreceptors.
Generally what do nerve fibres with smaller diameters tend to be associated with?
Small diameter means the nerve impulses will conduct slower
This is associated with nociceptors and thermoreceptors.
What is induction velocity positively correlated with?
Axon diametre
Name the sensory receptors from largest to smallest diametre
- Proprioceptors of skeletal muscles
- Mechanoreceptors of skin
- Pain and temperature receptors
- Itch receptors
Describe first pain
- Fast A-delta fibres
- Sharp or prickling
- Easily localised
- Occurs rapidly
- Short duration
- Mechanical or thermal nociceptors
Describe second pain
- Slow C-fibres
- Dull ache, burning
- Poorly localised
- Slow onset
- Persistent
- Polymodal nociceptors
What is the skin and deeper structures like muscles and viscera innervated by?
a rich vast network of peripheral nerves.
What are primary afferents?
Axons bringing information from the somatic receptors to the CNS
What are motor efferents?
Axons taking information from CNS to peripheral structures
Where do afferent nerves enter the spinal root from?
Afferents feed into the spinal cord via a spinal nerve and the dorsal root.
Where do efferent nerves leave the spinal cord?
Efferents leave the spinal cord via a ventral root and the spinal nerve.
Describe the route afferent nerves take from the sensory receptors
- Sensory receptor
- Spinal nerve
- Dorsal root ganglion cell
- Dorsal root
- Enter the dorsal horn
- Travel down the zone of Lissauer
Where does the first processing or Nociceptive fibres take place?
In the cell bodies within the dorsal root ganglion
Where do afferent terminal travel rev they enter the dorsal horn?
They enter the dorsal horn and travel up/down a short distance within the Zone of Lissauer
Where do afferent terminals synapse?
Afferent terminals synapse onto neurones within the superficial laminae of the dorsal horn.
What is the principle area that is innervated by nociceptors?
lamina I and lamina II (substantia gelatinosa)
Describe how Nociceptive Inputs from the viscera and skin converge?
Nociceptive afferents from internal organs (e.g. viscera) and the skin enter spinal cord through common routes and target overlapping populations of spinal neurons.
This ‘cross-talk’ accounts for referred pain whereby visceral pain is perceived as having a cutaneous source by the sufferer.
What is referred pain?
When a visceral sensation is felt as having a somatic source
Where do both the primary afferent impulses from the skin and viscera synapse and what can this lead to?
They both synapse at the dorsal root ganglion and this can lead to cross talk
What is a classic example of referred pain?
- People with angina can feel pain in the upper chest wall and left
- Appendicitis in its earl stages pain is refer to the abdominal wall around the naval
What does the ascending pain pathway process?
Processes afferent inputs from peripheral mechano-, thermal and polymodal nociceptors.
What type of pathway is the Ascending pain pathways
?
It is a contralateral pathway
Where is information relate to in the ascending pain pathway?
Information is relayed to the thalamus and then onto the somatosensory cortex.
What 3 components make up the ascending pain pathway?
Lateral (neo-) spinothalamic tract.
Spinoreticulothalamic tract (or paleospinothalamic).
Anterior spinothalamic tract (to RF and PAG).
Describe the ascending pain pathway
- Spinal cord
- Medulla
- Medial Leminiscus
- Midbrain
- Ventral posterior nuclear complex of thymus
- Cerebrum to the somatic sensory cortex
Name the fifth cranial nerve
The trigeminal nerve
Where do all three branches of the trigeminal nerve originate from?
They all originate in the semilunar (Gasserian) ganglion.
Name the 3 branches of the trigeminal nerve
- Ophthalmic branch
- Maxillary branch
- Mandibular branch
What does the Ophthalmic branch give feeling to?
face around the eye, bridge of the nose and the forehead.
What does the maxillary branch give feeling to?
The upper teeth and gums
The facial area below the eye
Above and including the top lip.
What does the mandibular branch give feeling to?
The bottom teeth, gums and tongue The skin below and including the lower lip.
Which system controls the pain and temperature pathway from the FACE and HEAD?
The trigeminal system
Describe the trigemini system
- Small diameter afferents descend in the spinal trigeminal tract to the brain stem.
- They Synapse with second-order sensory neurons in the pars caudalis.
- Axons then ascend contralaterally to thalamus in the trigeminothalamic tract (also called the trigeminal lemniscus).
- Projects to cortex via the ventral posteromedial nucleus.
- Innervates specialized structures e.g. tooth pulp innervated
Go through the structures involves in the Pain & Temperature pathway from the FACE and HEAD
- Pain & Temperature information fro the faces received
- Spinal trigeminal tract
- Spinal nucleus
- Caudal medulla
- Middle medulla
- Mid pons
- Trigemino thalmic tract
- Midbrain
- Ventral posterior medial nucleus
What type of experience is pain?
It is a complex sensory experience
What is phantom pain?
Pain and touch sensations with no sensory inputs
What is increased pain called?
hyperalgesia
What is allodynia?
touch -evoked pain
What is allodynia a feature of?
features of chronic pain syndromes & pathological pain.
What is the perception of pain subjected to?
The perception of pain is subject to central modulation.
What has the discovery of opiate receptors helped us discover?
The discovery of opiate receptors in the brain showed how morphine and heroin affect the body.
What has the research into how morphine and heroin affects put body led to?
Has led to the discovery of opiate-like chemicals produced in the body that control pain, immune responses, and other body functions.
Name our opiate receptors?
Mu
Kappa
Sigma
What are opiates derived from?
Opiates are derived from the juice of the opium poppy and have many benefits- but they also produce sobering side effects like addiction
What are some of the side effects of opiate?
Dizziness Nausea Constipation Dry mouth Blurry vision
Why are we responsive to cannabis and cannabis like drugs?
Because we have an endo-cannabinoid system
What can cannabis be prescribed for in the UK?
Parkinsons for tremors
Spasms from multiple sclerosis
What foe the endo-cannabinoid system do?
CB1 and CB2 receptors cloned
Inhibits behavioural responses to acute noxious stimuli. limits hyperalgesia and neuropathic pain
Probably acts at spinal and supra spinal sites
Describe our descending pathway?
Descending ‘endogenous analgesic’ pathways from periaqueductal grey matter and reticular formation decrease transmitter release from primary afferent terminals by an interaction with opioid receptors.
Where are tons of opiate receptors found?
periaqueductal grey matte and reticular formation
What percentage of the adult population endures chronic pain?
20%
Describe features of acute pain
skin abrasions deep tissue injury postoperative dental superficial burn
Describe features of chronic pain
inflammatory pain neuropathic pain neuralgias musculo-skeletal pain visceral cancer
After how many months is pain considered chronic?
3 months
Which receptors result in acute sensation?
Nociceptive Stimulation (thermal, mechanical chemical) They travel along C afferents to give us acute pain sensation
Which receptors result in Non-painful sensations?
Innocuous stimulation
(touch, pressure, brush)
They travel along A beta afferents to give us non- pain sensation
Which receptors result in Hyperalgesia and ongoing pain
Tissue/nerve damage, inflammation, disease
They travel along C afferents to give us Hyperalgesia and ongoing pain
Which receptors result in Allodynia
Innocuous stimulation
(touch, pressure, brush)
They travel along A beta afferents to give us Allodynia
What is allodynia?
Touch evoked pain
Why does hyperalgesia occur?
It is the phenomenon that occurs because damaged or inflamed is unusually sensitive
What can hyperalgesia be?
A reduced threshold for pain
An increased intensity of painful stimuli
Spontaneous pain.
Pain and touch sensations with no sensory inputs called what?
Phantom pain
